This invention relates generally to electric machines, and more particularly, to methods and apparatus for operating an electric machine.
At least some known high speed machines, such as a Lundell generator, benefit from eliminating active electrical components, such as field coils, from the rotor. More specifically, removing such components may improve the reliability of, and provide for, a more robust rotor design that does not require a mechanical support structure for such components. These machines have stationary field coils, and are generally fabricated from conventional conductors, such as, for example, copper or aluminum. Additionally, these stationary field coils are cooled by the same cooling medium as the rest of the machine.
It is well known that high speed machines, such as, for example generators or motors, generate heat that must be dissipated. To disseminate the heat, at least some known generators are equipped with cooling systems, such as, for example air, gas, and/or liquid ventilation systems. Typically, such ventilation systems cool both the stator and the rotor. It may be difficult to optimize the cooling of a generator that includes a stator, a rotor, with a ventilation system that provides cooling for both a rotor and a stator that are thermally coupled. However, the addition of a separate and independent cryogenic cooling system for cooling a stationary superconducting field coil would facilitate optimizing the cooling of the generator since it thermally decouples the field coil from the rest of the machine.